摘要:本文利用再分析资料与台站降水资料，比较了不同副高指数的变化特征，分析了不同指数与中国东部夏季降水的关系及相应环流变化。结果表明，副高指数可分为三类：绝对强度指数、相对强度指数和南北指数。绝对强度指数有上升趋势，对应5870 gpm等值线向西的扩张；相对强度指数有下降趋势，对应扰动位势0线的缩小；南北指数无明显趋势变化，表现为副高脊线基本围绕25°N振荡。不同副高指数对应的环流与降水异常表明，绝对强度指数虽然不能较好的描述副高局地的涡度变化，但其与东亚EAP（East Asia–Pacific，东亚—太平洋）型遥相关关系较好，在这种情况下，该指数与长江流域降水存在高相关，指数正异常时，华北偏干，长江中下游水汽辐合降水增加；反之降水型相反。相对强度指数能较好的描述副高局地的涡度变化，但其与EAP型遥相关关系较弱，因此相对强度指数与降水关系较弱，指数正异常时，降水中心仅出现在长江中游；反之，受异常偏北风影响，我国降水体现为北旱南涝。南北指数对副高局地的涡度变化以及EAP型遥相关都有较好表征，该指数与长江以南以及华北的降水有较好的相关性，指数正异常时，水汽大量向北运输，造成华北多雨而长江干旱；反之，相反的环流型使雨带移至华南。
关键词:副高指数/
夏季降水分布/
环流变化
Abstract:Based on the reanalysis data and monthly precipitation data, in this study we investigate the variabilities of the western North Pacific subtropical high indexes (WPSHI) and discuss the relationship between WPSHI and summer precipitation in eastern China, together with the related circulation changes. Results show that WPSHI can be divided into three categories, namely, absolute intensity index (ASI), relative intensity index (RLI), and north-south index (NSI). The upward trend in ASI is associated with the expansion of the area covered by 5870 gpm isolines. The downward trend in RLI accords well with the shrink of the 0 gpm isoline of the eddy geopotential height (EGH). The lack of variations in NSI indicates that the ridge of WPSH oscillates around 25°N. Depicted by circulation anomalies and precipitation patterns, ASI cannot reflect the variation of local relative vorticity of WPSH, but it has close relationship with EAP (East Asia–Pacific) pattern. In this case, ASI has the best correlation with the precipitation in the Yangtze River basin. In the years when the ASI is high, north wind anomalies favor less rainfall in northern China, while the water vapor convergence strengthens the precipitation along the Yangtze River, and vice versa. RLI can better describe the variation of the local relative vorticity of WPSH, but it has a weaker relationship with the EAP pattern and the precipitation in eastern China. In the years when the RLI is high, precipitation center appears in the middle reaches of the Yangtze River. Conversely, drought occurs in the north of Yangtze River with anomalous north winds over China. NSI can describe both the variation of local relative vorticity of WPSH and the EAP pattern and has a high correlation with precipitations in southern and northern China. In the years when the NSI is high, enhanced vapor flux leads to flood in northern China and drought along the Yangtze River. When the NSI is low, the precipitation is trapped in southern China, as resulting from a reversed circulation pattern.
Key words:Western North Pacific subtropical high indexes/
Summer precipitation pattern/
Circulation anomaly
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